Vacuum tube



Jan. 24, 1928.

1,657,221 H. E. METCALF ET AL VACUUM TUBE Filed March 25, 192k;

.V 9 H l 8 k 6 Y 5 I E I I J 7 5' Eli/.17 26 El 1 Z J /6 3 3 fizz/enters Patented Jan. 24, 1928.

UNITED STATES PATENT OFFICE.-

HERBERT E. METCALF, 'OF SAN LEANDRO, AND VALENTINE FORD GREAVES, OF OAK- LAND, CALIFORNIA, ASSIGNORS TO TIIE IMAGNAVOX COMPANY, OF SAN FRAN- CISCO, CALIFORNIA, A CORPORATION OF ARIZONA. v

vacuum TUBE.

Application filed March 23, 1925. Serial No. 17,580.

This invention relates to vacuum tubes, particularly of the three electrode type for use as rectifiers, amplifiers and electric wave generators. The object of the invention is to improve the construction of such a dev ce, whereby it is made incapable of generating the so called mierophonic noises to which all such devices are more or less subject, and whereby extreme resistance to external shocks is obtained along with permanent and definite alignment of the filament in relation to the control electrode.

A further object of the invention is to support the filament in such a way that it is not subject to vibrations independent of the control electrode, as is common in the ordinary construction of such devices. In investigating the cause of the internal noises of such a tube, we have found that while noises appearing in the output circuit of the device are small, nevertheless when the device is used as a detector of electric wave and the output amplified, the noises are objectionable. On' further investigation we have found that while the causes of these microphonic noises are varied, one of the important ones is due to the fact that the filament is supported separately and apart from the control electrode, and when lightly tapped or subjected to slight shocks, a microphonie noise or sound in the output circuit is caused.

Inasmuch as this noise has been found due to a changing of the filament position rela tive to the control electrode contained therein, our present invention deals with a new construction, whereby this movement is eliminated, and therefore such noises as this movement may cause are also eliminated.

A further object of our invention is to provide a support for the top of the filament, made out of an insulating flexible material, so that the stretch of the filament when heated may be taken up without interfering with the action of the device to reduce microphonic noises. A still further object of the invention is to arrange this filament support rigidly attached to the control electrode, so that the filament is always in a very definite relation to the control electrode during assembly and thereafter. The total construction makes the assembly such that the filament must always be in the exact position desired, and can not by any means be thrown out of its proper alignment.

In easeit is not desired to use a flexible insulating device to support the apex of the filament, we have arranged the construction so that a piece of non flexible insulating material, such as mica, can be attached with a pivot to the control electrode and the spring to make up for the expansion of the filament being taken care of by an auxiliary conducting spring which bears against the non-conducting portion of the filament support. Whether the filament support be fiexible or non-flexible, the results obtained in either case are identical.

In the accompanying drawing We have shown certain specific embodiments of our invention, but it will be understood that the invention. can be otherwise embodied and that the drawing is not to be construed as defining or limiting the scope of the invention, the claims appended to the specification being relied upon for that purpose.

Referring to the figures of the drawing:

ig. 1 is a perspective view of our improved vacuum tube, certain parts being broken away to more clearly illustrate the invention.

Fig. 2 is a side elevation of a portion thereof.

Fig. 3 is an edge view of Fig. 2.

Fig. 4 is a View similar to Fig. 2 but showing a modified form of our invention.

Fig. 5 is a view similar to Fig. 1, ,but showing our improvement applied to another type of radio vacuum tube.

Fig. 6 is an edge view thereof.

Fig. 7 is a view similar to Fig. 4, but showing our improvement applied to a vacuum tube of the type shown in Fig. 5.

Referring first to the construction of our invention as shown in Figs. 1, 2 and 3, 1 indicates-the bulb and 2 the base of a radio vacuum tube. Mounted on the supporting stem 3 within the tube are two plates 4, a control electrode 5 and a filament '6.

In the usual construction of these tubes all the electrodes are supported on wires extending intothe stem 3. In our improved construction, the lates 4 are supported by wires 4 and the e ectrode 5 is supported by a wire 5' both on the stem 3. The filament 6, however, is supported on the electrode 5 in the manner hereinafter described. The ends "of the filament are connected to terminals 7 extending into the base 2.

As illustrated in Figs. 1, 2 and 3, the filament 6 is supported within a V slot in the electrode 5. This slot divides the electrode into three upwardly extending tongues, We mount an upwardly and downwardly extending spring element 8 on the upper ends of these tongues. The upper end of this element is folded over in a manner to hold a filament supporting strip 9 of mica therein in a horizontal position. The free end of this strip 9 extends over the slot and beneath the looped end of the filament. The fiat mica strip 9 as held in a. horizontal plane in this construction provides a resilient support for the filament.

In Fig. 4.- the filament is supported onithe control element 5 but in a somewhat modified manner. In this construction, the flat mica stri 9 is held on edge in a vertical plane. (lhe end thereof is supported by an upwardly extending portion 10 on the electrade 5. The strip extends beneath the filame loo as in Fig. 1, and the other end is supnorte by a spring arm 11 secured to the eh zrode 5 at 12.

In Figs. 5 and 6, we have illustrated a form of our invention shown in Figs 1, 2 and y 3 as applied to another type of vacuum tube.

In this construction the control element comprises a air of vertical wires 13 having a wire fiel 14 formed therearound. A spring element 15 and a'mica strip 16, like those shown in Figs. 1, 2 and 3, are mounted on the control element and support the filament 17 within the field 14 in a like manner.

In Fig. 7 is illustrated how the form of our invention shown in Fig. 1 can be applied to a tube of the form shown in Fig. 5. The filament 18 is supported by a mica strip 1.) supported at one end on the control element wire 20 and at its other end by a spring 21 also mounted on the wire 20.

It is believed that the construction, operation and several advantages of our invention will be apparent from the above description taken in connection with the drawing. In our improved construction the filament is supported directly on the control electrode, whereas heretofore these elements have ordinarily been supported independently on the base 3 within the bulb 2. By supporting the filament on the control electrode the same is held permanently and definitely in alignment relative to the electrode and the two elements are not subject to vibrations one relative to the other. Such relative vibrations of these parts have heretofore caused considerable disturbance since they directly cooperate with each other in'opcration. It is obvious that in'our construction any vibration of the tube will tend to vibrate these two elements as a unit.

The construction is also suchas to allow for contraction and expansion of the filament due to heat. The mica strip, when mounted horizontally flat as in Figs. 1, 2, 3, 5 and 6, acts to support the filament rcsiliently. This strip in combination with the spring supporting the strip cooperates with the filament to stretch the same when heated and hold it in proper relation to the elec trode. In Figs l and 7, the mica strip does not of itself operate to resiliently support the filament, but the long supporting spring for the mica strip performs this function. The improved construction also has other advantages such as simplicity and definiteness of manufacture and assembly as have been heretofore referred to.

Having thus described our invention, what we claim and desire to secure by Letters Patent is:

1. A vacuum tube of the character described, having a plurality of electrodes therein, one of such elements being a platelike member, a looped filament adjacent and cooperating with such member, and resilient insulating means carried by the said member and resiliently supporting the looped end of the filament.

2. A vacuum tube of the character described, having a control electrode therein, a filament adjacent and cooperating with the electrode, and means including a flat insulating spring element carried by the electrode transversely of and supporting the filament in a manner permitting expansion and contraction of the filament.

3. A vacuum tube of the character dcscribcd, having a control electrode therein, a filament adjacent and cooperating with the electrode and an insulating bar carried by the electrode extending transversely of and yieldingly supporting the filament.

4. A vacuum tube of the character described, having a slotted electrode therein, a filament in the slot, and a resilient insulat- Ill ing element carried by the said electrode and supporting the filament in the slot.

5. A vacuum tube of the character described, having a control electrode therein, a filament adjacent and cooperating with said electrode, a fiat mica spring-element attached to the electrode and sup orting the filament in a manner to keep t e filament under tension during contraction and expan- 7. In a vacuum tube of the character desion thereof. scribed, a resilient support for the filament 6. A Vacuum tube of the character (10- carried by a second electrode of the tube, 10 scribed, having a resilient insulating support said resilient support being composed entire- 5 for the filament attached to the control elec ly of a non-conducting material.

trode, said resilient insulating support con- HERBERT E. METCALF. sisting of a flat strip of mica. VALENTINE FORD GREAVES. 

